An apparatus for determining the ametropia of an eye is suitable to determine the visual defect of an eye. By way of example, the determined visual defect of an eye of a patient can be the basis for a prescription of visual aids, such as, for example, spectacles or contact lenses, in order to correct the visual defect of the eye. The apparatus makes an optical measurement at the eye in order to determine the ametropia. Data which represent the ametropia of the measured eye are obtained by the optical measurement. These data typically represent a magnitude of a spherical visual defect and a magnitude and axis of an astigmatic visual defect of the eye. Furthermore, the determined ametropia of the eye can form the basis for planning a surgical intervention, such as, for example, a LASIK method, on the eye in order to improve the visual acuity thereof by changing the structure of the cornea with the aid of a laser beam. The optical measurement can be the apparatus directing an illumination light beam towards the eye in order to illuminate a small spot of the retina with light. Some of this light is scattered or reflected at the retina such that the small illuminated spot on the retina serves as a point light source for measurement light. This measurement light emerges from the eye as a light beam which is formed by the optical components of the eye, such as the vitreous humor, the lens and the curved cornea. This measurement light beam can be supplied to a detector for analysis purposes in order to deduce the optical properties of the optical components of the eye and hence the ametropia of the eye. By way of example, the detector can be a wavefront sensor, such as, for example, a Hartmann-Shack sensor. During the measurement using a wavefront sensor, it is possible to obtain data characterizing the ametropia of the eye, the data going beyond the magnitude of a spherical visual defect and the magnitude and axis of an astigmatic visual defect data usually used for the prescription of spectacles and enabling the correction of higher-order refractive errors, for example using the LASIK method.
In practice, it was found that it is not always simple to evaluate the detection signals obtained by the detector and to obtain therefrom data which represent the actual ametropia of the measured eye with high confidence.